Shadow bruja Ren Santiago made her good friend Ah-Puch, the Maya god of death and destruction, promise to end her life before she was forced to live as queen of the evil Lords of Night. In order to get her life back, Ren negotiates with Ixtab, queen of Xibalba. Ixtab offers her ten days aboveground to retrieve the crown of jade and shadow. If Ren fails, she will return to the darkness for eternity.

On a trip to visit her grandparents in Japan, Tessa Miyata inadvertently releases the spirit of an evil samurai god who wants to destroy Tokyo, and stumbles upon a hidden part of the city where gods and mythological creatures walk among humans.